1. Field of the Invention
The present invention relates to a control system/method for controlling the engagement of positive jaw clutches in an at least partially automated vehicular mechanical transmission system. More particularly, the present invention relates to a control system/method for an automated vehicular mechanical transmission system which will cause or bias the transmission jaw clutches to engage at a time when input shaft speed is expected to be within a range of true synchronous speed, called the synchronous window, the extent of which is a function of the numerical value of the target gear ratio until a minimum value is reached.
2. Description of the Prior Art
Fully or partially automated mechanical transmission systems for vehicles, such as heavy duty tractor--semitrailer vehicles, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,614,126; 4,648,290; 4,676,115; 4,784,019; 4,874,881; 4,899,607; 5,050,427 and 5,136,897, the disclosures of all of which are incorporated herein by reference. Briefly, these automated transmission systems typically utilized sensors to provide information such as drive mode or shift selection, throttle pedal position, currently engaged ratio and engine, input shaft and/or output shaft speeds to a controller. The controller, typically microprocessor based, would process these inputs according to predetermined logic rules to issue command output signals to various actuators such as an engine fueling device, a master clutch operator and/or a transmission shift actuator. Engine fueling manipulation, an input shaft or engine brake and/or a power synchronizer were typically used to cause the input shaft and its associated gearing to rotate at a substantially synchronous rotational speed relative to the output shaft rotational speed and target gear ratio.
In view of the known response times for the various actuators, as the input shaft speed ("IS") approached the synchronous window, i.e. the product of output shaft speed times the numerical value of the target gear ratio (OS *GR.sub.TARGET) plus or minus an acceptable value (usually about.+-.40 RPM), the jaw clutches associated with the target gear ratio were commanded to engage with the expectation that the expected input shaft speed (IS.sub.E) would be within the acceptable range as the target ratio jaw clutch members came into initial engagement.
While the prior an vehicular automated mechanical transmission system controls were generally satisfactory and provided well synchronized jaw clutch engagement, they were not totally satisfactory as, at the lower speed ratios (higher numerical reduction ratios), the synchronous windows were more restricted than necessary making achieving synchronous more difficult or time-consuming than necessary.